A phone call is a very efficient way for quick interpersonal communication. When a subscriber goes out of a province, inter-provincial roaming requires extra charge. When the subscriber goes abroad, international roaming fee for a phone call will become very expensive. There are generally two solutions in a case that the subscriber wants to meet his/her demand for calling when roaming. A first solution is that the subscriber opens international roaming or inter-provincial roaming by an operator, and the subscriber can make a phone call when roaming, but a disadvantage of the first solution is relatively higher roaming fee for the phone call charged by the operator. A second solution is that the subscriber rents or purchases a mobile phone locally after going abroad, and makes a phone call by using a network provided by a local operator, but a disadvantage of the second solution is that the subscriber needs to overcome a language barrier so as to rent or purchase the mobile phone, besides, the whole process is time-consuming and toilsome, and especially for multi-country tourism, it is more bothersome and costly.
Therefore, it is expected to provide the subscriber with data transmission service of the operator at a roaming place conveniently, in order to save the roaming data service fee.